Average Proportion Of Polymorphic Loci Research Articles

Characterization of diversity and genetic structure in natural populations of Stryphnodendron adstringens (Mart.) Coville by means of allozyme markers

The S. adstringens, a typical Cerrado (Brazilian savannah) tree, is used because of its medicinal and tanning properties. Because of the still incipient genetic knowledge of the species, the objective of this work was to characterize the diversity and genetic structure of S. adstringens by using allozyme markers. Seeds were collected in five Brazilian mesoregions, in which 627 individuals in 16 populations in the states of Minas Gerais and Goiás were sampled. Fourteen isoenzyme systems were assessed, out of which seven were polymorphic with a total of 10 loci and 28 alleles. Average genetic diversity (H) was 0.226, average proportion of polymorphic loci (P) was 68.75, average number of alleles per polymorphic locus (AP) was 2.65 and effective number of alleles (Ae) was equal to 1.29. The results of total fixation index (F= 0.003), within population fixation index (f =-0.114) and genetic differentiation measure (θ =0.105) were not significant, which shows the inexistence of genetic structure. Two principal groups were found in the cluster analysis (UPGMA), where the first one was formed by the population of State Park (PE) of Rio Preto (MG) and the other, by the other populations. If the population of PE of Rio Preto is excluded from the analysis, G ST is drastically reduced from 0.077 to 0.026. Thus, approximately 2/3 of the total value of G ST found in S. adstringens was due to the variation among the population of PE of Rio Preto and the other populations. Overall, the values of H and P found in S. adstringens are compatible with the ones found in typically distributed tropical trees. On the other hand, by excluding the population of PE of Rio Preto, the value of the G ST genetic differentiation measure was smaller than the one found in native tropical trees from temperate zones. The similarity between the assessed populations shows that the gene flow is still high enough to avoid genetic differentiation, at the local level, at least.

Genetic diversity and population structure in Harpadon nehereus based on sequence-related amplified polymorphism markers

In this study, the genetic diversity among ten populations of the Bombay duck was studied on the basis of sequence-related amplified polymorphism (SRAP). The ten populations were collected from the East China Sea and South China Sea areas. A total of 98 loci were obtained from 292 individuals using eight SRAP primers. The average proportion of polymorphic loci, genetic diversity (H), and Shannon's information index were 75.20%, 0.2478, and 0.3735, respectively. Nei's genetic distance and Shannon's information index between the ten populations ranged from 0.0410 to 0.3841 and from 0.2396 to 0.4506, and the averages Nei's gene diversity index (H = 0.2478) and Shannon's information index (I = 0.3735) at the population level were high. AMOVA showed that most of the variation was within populations (71.74%), and only 28.26% of the variation was between populations. The neighbor-joining tree based on genetic distance revealed that significant genealogical structure existed throughout the examined range of the Bombay duck. The results demonstrated that SRAP marker was an effective tool for the assessment of genetic diversity in the Bombay duck. The results could be used for further protection of the germplasm resource of the Bombay duck.

GENETIC DIVERSITY OF Agave cupreata TREL. & BERGER. CONSIDERATIONS FOR ITS CONSERVATION

Agave cupreata Trel. & Berger is an endemic plant naturally distributed in the Balsas Depression, a semiarid region in the states of Guerrero and Michoacán in Southwestern México. Their populations are heavily decimated because mature individuals just before their single life flowering period are harvested to produce mezcal, an alcoholic beverage. The genetic variation among and within 12 natural populations was examined for nine isozyme loci. Results indicate high average proportion of polymorphic loci (93 %) and expected heterozygosity (He = 0.467), with an excess of observed heterozygotes in relation to Hardy-Weinberg expectations (Ho = 0.521, FIS = -0.1179). These results represent the largest heterozygosity reported for Agave species endemic to México. There is also a statistically significant genetic differentiation among populations (FST = 0.042). An UPGMA dendrogram reveals the absence of a geographic pattern, as confi rmed by a Mantel test (r = -0.110, P = 0.769), which did not show significant isolation by distance. Estimated minimum viable effective population size was very large (Ne =16,165), larger than in any other known natural population. To protect the natural genetic variation, it is suggested to design and manage A. cupreata natural populations as forest genetic resource conservation units (FGRCUs) using realistic and modest Ne sizes, perhaps between 500 and 5000 plants, ideally with intermediate plantations that could serve as pollinator corridors. Commercial plantations and ex situ FGRCUs need to be established to gradually develop a sustainable management, perhaps at higher altitudes than current locations, as a management measure for adaptation to the climatic change.

Allozyme variations in six natural populations of scots pine (Pinus sylvestris) in Turkey

Genetic variation in six natural populations of Scots pine (Pinus sylvestris L.) was determined with isoenzyme analyses. For this purpose, haploid female gametophytes of seeds and horizontal starch gel electrophoresis technique were used. A total of 17 loci and 58 alleles were observed in studying 10 enzyme systems. The average proportion of polymorphic loci for populations ranged from 58.8% to 70.6%. The average number of alleles per locus per population was 2.65. The mean estimated expected heterozygosity (He) of populations was 0.294. A rather high proportion of genetic diversity (96.4%) was due to within-population variation and the remaining (3.6%) was due to variation among populations. The level of gene flow (Nem) was found to be 6.69 per generation. Nei’s genetic distance coefficient ranged from 0.006 to 0.027 (mean 0.017) among all possible population pairs. The mean value of Nei’s genetic distance is similar to the values reported for other European Scots pine populations. The low mean value of Nei’s genetic distance among populations is enough to explain low interpopulation variation. According to genetic variation parameters, three out of six populations (Akdagmadeni-Yozgat, Refahiye-Erzincan and Vezirkopru-Samsun) appear to be preferable populations for genetic conservation and forest tree breeding programs.

Comparative analysis of genetic diversity using molecular and morphometric markers in Andrographis paniculata (Burm. f.) Nees

Andrographis paniculata is a medicinal plant of immense therapeutic value. The present study was aimed to elucidate its genetic diversity based on morphochemical and RAPD markers from 53 accessions belonging to 5 eco-geographic regions. Analysis of variance and D 2 statistics revealed significant differences in all the metric traits and sufficient inter-cluster distances indicating considerable diversity among the accessions. The complementary approach of RAPD was used to evaluate the genetic dissimilarities among all the accessions using 6 highly polymorphic primers. The average proportion of polymorphic loci across primers was 96.28%. The molecular genetic diversity based on Shannon index per primer averaged 5.585 with values ranging from 3.08 to 8.70 indicating towards wide genetic base. RAPD based UPGMA and D 2 cluster analysis also revealed that various accessions available in different eco-geographic regions might have originated from native places of wild abundance. Similarity matrices were generated for molecular markers and morphometric data to determine the degree of congruence between the two. A highly significant but low correlation (r = 0.547, P < 0.001) was obtained thus implying the correspondence between the two. The species is hermaphroditic and a habitual inbreeder. The present study yielded a typical triangular congruence between its breeding system, morphometric traits and RAPD markers thus elucidating the usefulness of complementary approaches to make diversity analysis more explanatory and purposeful for optimum genetic amelioration and effective conservation of its genotypic variability.

Genetic structure of a rare European conifer, Serbian spruce (Picea omorika (Panč.) Purk.)

Genetic variation in 13 populations of a Balkan endemic, Serbian spruce (Picea omorika (Panc.) Purk.), was investigated using 16 isozyme loci. Serbian spruce is characterized by low levels of genetic variation (average proportion of polymorphic loci was 20.9% and average expected heterozygosity was 0.067). In most populations, a significant surplus of heterozygotes was observed, indicating a strong selection against inbreds. In the largest populations, fixation indices were positive, probably due to within-population differentiation and the associated Wahlund effect. Despite a strong overall differentiation (FST=0.261), no geographical trends in the genetic variation could be identified. Genetic drift caused by small effective population sizes and a strong fragmentation is the most plausible explanation for such variation patterns. A Bayesian analysis of population structure revealed the existence of two clusters, which are supposed to be possible remnants of ancient differentiation within a large range of the predecessor of Serbian spruce, Picea omoricoides Weber. Ex situ conservation measures, namely establishing seed orchards from trees of mixed origin, are proposed as a necessary complement to in situ protection of natural stands.

The Effects of Founding Events and Agricultural Practices on the Genetic Structure of Three Metapopulations of Globodera pallida

To assess the genetic constitution of the Globodera pallida populations in the Netherlands and the effects of agricultural practices, three geographically separated metapopulations, in total consisting of 226 local populations, were analyzed by two-dimensional gel electrophoresis (2-DGE) of total proteins. This technique allows the accurate assessment of allele frequencies in homogenates of mixtures of individuals. Based on the estimated average heterozygosity, the average proportion of polymorphic loci and the average number of alleles per locus, the genetic diversity among 226 local G. pallida populations was small. The small genetic basis of G. pallida in the Netherlands will facilitate the identification of Solanum genotypes with a broad and durable resistance to G. pallida. Instead of clusters of local populations with unique alleles, a continuous range of allele frequencies was observed. Analysis of the three metapopulations by the Shannon-Weaver index and Nei's G(ST) revealed that the metapopulation from a region with sandy-loam soils was clearly distinguishable from the remaining two; the local populations within this metapopulation were more similar and the genetic diversity within the individual local populations was significantly higher than the local populations from the two remaining regions. These regions are characterized by wider crop rotation schemes and a very limited use of nematicides. The less intensive cultivation of potatoes in these regions with sandy-clay soils resulted in relatively little variation within and more variation between local nematode populations. To our knowledge, the effects of agricultural practices on the genetic constitution of potato cyst nematode populations have not been pinpointed before.

Allozyme Variation in Four Geographic Areas of Cinnamomum kanehirae

The once dominant endemic broadleaf tree species In Taiwan, CInnamomum kanehlrae Hay., has become a rare and endangered species due to overcutting. A done bank, consisting of at least 220 clones collected istandwide, was established at the Uukuel station, Taiwan Forestry Research Institute. Genetic diversity wtthln and genetic differentiation among four geographic areas of C. kanehlrae were Investigated using 164 clones collected from the clone bank. Seven out of the 11 loci examined were polymorphic. The average proportion of polymorphic loci per area was 51% at the 99% criterion for polymorphism. Mean expected heterozygosity ranged from 0.188-0.261 In the different areas, and 0.238 at the species level. On average the percent heterozygous loci per individual ranged from 13.9-21.6%, the number of alleies per locus ranged from 1.7-1.9, and the effective number of alleies per locus ranged from 1.34-1.54 at the area level. The much higher expected heterozygosity and higher number of aJtofes per locus compared to other local woody species investigated may support the hypothesis that Taiwan was a distributional center of CInnamomum. Partitioning the genetic variability Into withinand among-geographlc area components with F statistics and gene diversity analysis led to an estimate of wtthin-area variation amounting to 88% of the total variation. A slight barrier to gene flow among areas could be due to the large seed size and to Insect pollination. The limitation of seed dispersion, erratic flowering times, and several subpopulations wtthln the same geographic areas may contribute to the lower levels of observed heterozygosity than expected heterozygosity among the seven polymorphic loci, indicating some degree of Inbreeding and the Wahlund effect and thus a slight deficiency of heterozygotes (Fto = 0.157). Area 4, located in southeastern Taiwan has a much lower elevational distribution and showed a higher proportion of polymorphic loci, implying that genetic variation of area 4 may have developed under different climate conditions.

Allozyme and morphological variability, outcrossing rate and core collection formation in lentil germplasm

A survey of qualitative genetic variation at 3 morphological trait loci, 17 isozyme loci and a putative isozyme locus (amylase) was made for 105 lentil (Lens culinaris Medikus) germplasm accessions from Chile, Greece and Turkey. New alleles were found for Lap-1, Me-2, Pgm-c, Pgm-p and 6-Pgd-c. The average proportion of polymorphic loci per population was 0.19, with a range of 0 to 0.42 over populations. Germplasm from Chile was equally variable to that from Greece and Turkey on the basis of individual loci and in a multilocus sense, despite its post-Columbus introduction to the New World. Evidence was found from associations between allelic states at different loci of a complex multilocus structure of lentil populations. A single multilocus genotype represented 10.2% of all plants sampled. The rate of outcrossing varied from 2.2% and 2.9% in Turkish and Greek landraces to 6.6% among Chilean populations. Using the survey data, a random sampling strategy for core collection formation was compared with two stratified sampling methods. The advantage of stratified sampling over random sampling was only significant at P=0.28.

Genetic Variability and Biochemical Systematics of Domestic and Wild Cat Populations (Felis silvestris: Felidae)

Genetic variability and phylogenetic relationships among domestic and wild populations of cats were studied by allozyme electrophoresis. Tissues were obtained from 67 specimens of European wild cats (Felis silvestris silvestris), African wild cats (F. s. libyca), and domestic cats from Italy; 54 presumptive loci were resolved. The average proportion of polymorphic loci and heterozygosity were P̄ = 0.11, H̄ = 0.042 in the wild cat, and P̄ = 0.20, H̄ = 0.066 in the domestic cat. Despite reduced genetic variability, local populations of wild cats were not inbred, as indicated by nonsignificant FIS values. Both FST and Nei's genetic distances between domestic and wild populations were low (F̄ST = 0.04; D̄ = 0.0082). Dendrograms indicate that the domestic cat belongs to the African wild cat lineage, which supports current hypotheses on cat domestication. Based on the genetic evidence, we suggest that the European wild cat, the African wild cat, and the domestic cat belong to the same polytypic species (Felis silvestris Schreber, 1777), and that the European and African wild cats diverged approximately 20,000 years ago.

Inheritance of isozyme variants in leaf tissues of hinoki, Chamaecyparis obtusa, and allozyme diversity of two natural forests.

Isozyme variation found in leaf tissues of hinoki, Chamaecyparis obtusa, were investigated using polyacrylamide vertical slab gel electrophoresis. Twelve enzyme systems were examined in selfed and crossed families to detect marker genes, and electrophoresis banding variants for 10 of the 12 enzyme systems were observed. Judging from the segregation data, 14 Ioci were identified. The genetic variation of three populations of two natural forests was surveyed using these isozyme loci. The average proportion of polymorphic loci (95 % criterion) was 56.4%, the mean number of alleles per locus was 2.00, and the mean expected heterozygosity was .228. The results of the gene diversity analysis and genetic distance indicated these populations are differentiated little from each other.

Genetic variation in the Iberian toothcarp, Aphanius iberus (Cuvier &amp; Valenciennes)

The Iberia toothcarp, Aphanius iberus (Cuvier & Valenciennes), is endemic to the brackish water marshes of the Spanish Mediterranean and southern Atlantic coasts. This species is in danger of becoming extinct due to the degradation or destruction of its habitats by man, and the introduction of the mosquitofish, Garnbusia afJinis Baird & Girard, for the purpose of controlling mosquitoes. Here we present the first results of genetic analysis of several populations of A. iberus, directed towards avoiding the extinction of this species. Samples were taken from four localities placed in the extreme north of the area of distribution of A . iberus. Two of these localities (A1 and A2) are in a brackish marshy zone some 300 km to the north of the River Ebro delta, known as the Aiguamolls de 1'Emporda. The other two (D1 and D2) are brackish lagoons from the Ebro delta itself. Fish were captured with a dipnet from the banks and stored at -80 C until the moment of analysis. The electrophoretic methodology and interpretation of the zymograms will be described elsewhere. Altogether 25 loci were detected, four of which were polymorphic to the criterion of 99% in at least one of the localities: adenylate kinase (Ak, E.C. 2.7.4.3), glucosephosphate isomerase (Gpi, E.C. 5.3.1.9), isocitrate dehydrogenase (Zdh, E.C. 1.1.1.42) and phosphoglucomutase (Pgrn, E.C. 5.4.2.2). The allelic frequencies in the four polymorphic loci are summarized in Fig. 1. The average proportion of polymorphic loci ( P ) is 0.095, quite similar to the 0.07 1 deduced from the earlier work of Scholl et al. (1978), and the mean average heterozygosity (H) is 0.029. These levels of genetic variation are smaller than levels obtained in other species of endangeredcyprinodontids: in the desert pupfish, Cyprinodon rnacularius Baird & Girard, P=O.185,H=O.O42 (Turner, 1983); and in the Near East toothcarp, A . dispar Riippell, P = 0.178, H = 0-049 (Nevo et al., 1984). As may be observed in Fig. 1, the genetic variation (polymorphic loci and number of alleles per locus) is less in the samples taken from the Aiguamolls than in those taken from the River Ebro delta, possibly a result of the marginal position of these populations in the area of distribution of this species. The analysis of genetic diversity has brought to light a high level of differentiation between populations (22%), of which 1 YO is between localities within areas, and 21 % is between the Aiguamolls and Ebro delta areas. The genetic variation is the result of years of evolution and represents the evolutionary legacy of a species, the loss of genetic variation is generally expected to increase the probability of extinction. Thus, an understanding of the population genetic structure of a species is an aid in formulating a genetkally rational conservation programme. When substantial divergence exists among geographic groups of populations, maintaining genetic diversity requires the continued existence of populations in each region. Refugia are an important component of the effort to preserve endangered species, and refugium populations should serve as a potential source from which many other natural populations may be eventually re-established. In the light of our results showing low genetic diversity between locations within areas (1 %) and substantial genetic diversity between areas (21 YO), an adequate conservation policy for A . iberus in the zones studied should be based on the declaration of at least one natural refugium in each area (Aiguamolls de 1'Emporda and the 233

Isozyme Variation between Geographic Populations of the Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)1

Genetic divergence of 12 populations of the Colorado potato beetle, Leptinotarsa decemlineata (Say), was studied by starch gel electrophoresis to examine enzyme products of 11 genetic loci (ACPH, EST-1, EST-2, FUM, G-6PDH, GOT, α-GPDH, IDH, MDH, ME, and SOD). Mean heterozygosity of these populations was 0.206, with an average proportion of polymorphic loci of 0.515. The 11 populations from the United States and Europe were similar genetically, with an average genetic distance of 0.022 and a fixation index of 0.068. Heterozygosity of the Mexican population was significantly lower than that of the other populations. One locus (SOD) was diagnostic, separating the Mexican population from the others. Average genetic distance between the Mexican population and the other 11 populations was 0.212, indicating that it may be a distinct subspecies. Genetic distance between L. decemlineata and L. haldemani Rogers was 0.439. The moderately high levels of genetic variability found in the Colorado potato beetle suggest that the species is able to exploit a wide range of food plants without further adaptation.

Genetic variation of allozyme and quantitative traits in a selected Douglas-fir [ Pseudotsuga menziesii var. menziesii (Mirb.) Franco] population

The genetic variation at 27 allozyme loci and seven different seedling traits were studied in a coastal stand of Douglas-fir [ Pseudotsuga menziesii var. menziesii (Mirb.) Franco] with respect to different elevation classes. The average proportion of polymorphic loci per elevation class was 0.54 ± 0.06 and the average proportion of heterozygous loci per individual was 0.17 ± 0.02. The isozyme data showed that the amount of genetic polymorphism varied considerably between loci and the amount and pattern of genetic variation for most loci were similar among the different elevational classes although some loci had large differences among elevational classes. Seven % of the total genic diversity was attributed to interelevational differentiation while the remaining 93% resided within the different elevational classes. Good agreement occurred between the isozyme data and quantitative information obtained from half-sib families of the same trees used for the isozyme analysis. The analyses of variance for the studied traits gave the same general trend and variation within the different elevational classes varied between 94 to 100%. In general, both the quantitative and the isozyme studies showed that the majority of variation resided within and not among the different elevation classes. Using these two different approaches in assessing variation in natural population is recommended.

Enzyme variation in natural populations of Sitka spruce (Piceasitchensis). 1. Genetic variation patterns among trees from 10 IUFRO provenances

Genetic variation at 24 enzyme loci was studied for 10 IUFRO populations of Sitka spruce (Piceasitchensis (Bong.) Carr.). The average proportion of polymorphic loci per population was 0.51 ± 0.02 and the average proportion of heterozygous loci per individual was 0.15 ± 0.03. The following generalizations were advanced: (1) the amount of genetic polymorphism varied considerably from locus to locus; (2) many populations were similar in the amount and pattern of genetic variation for most loci; (3) but some loci had large differences among populations.Eight percent of the gene diversity was attributed to interpopulation differentiation; 92% of the total gene diversity resided within populations. Pairwise comparisons of genetic distances averaged 0.014, a value which reflected very little differentiation between geographic sources.

Enzyme variation in populations of ayu, Plecoglossus altivelis.

Variation of 11 enzymes and the muscle protein presumably controlled by 19 loci was analyzed by electrophoresis in 506 individuals of Ayu, Plecoglossus altivelis, from 9 natural populations. Six loci (32%) were polymorphic in one or more populations. The number of alleles per locus in the average population was 1.13. The average proportion of polymorphic loci and the average heterozygosity were 9.1% and 0.6%, respectively. These estimates of genic variability in Ayu are lower compared to those for other species. At polymorphic loci, landlocked populations in Lake Biwa were homogeneous in allele frequencies, and amphidromous populations were similarly homogeneous on the whole. But between these two forms of Ayu, there were significant differences in allele frequencies at two loci (Me-l and Pgm).

Evolutionary Divergence in the Genus Taricha (Salamandridae)

Genetic variation at 18 loci which code for enzymes and proteins has been assessed by means of starch gel electrophoresis in the species and subspecies of the genus Taricha. The average proportion of polymorphic loci per population ranges from 20.4% in T. t. torosa to 41.2% in T. granulosa while the proportion of loci at which an individual is heterozygous ranges from 5.3% in T. t. torosa to 10.9% in T. rivularis. Genetic similarity (I) and genetic distance (D) statistics were computed from allelic frequencies. The mean I and D values between consubspecific populations are 0.972 ? 0.009 and 0.029 ? 0.010, respectively. A southern population of T. t. torosa has a D value of 0.109 when compared to northern populations of T. t. torosa; such genetic divergence is comparable to that found between T. t. sierrae and the northern populations of T. t. torosa (D = 0.126). This supports preexisting evidence of divergence between the northern and southern populations of T. t. torosa and suggests that this species may consist of three subspecies. The mean I and D between the species are 0.633 ? 0.013 and 0.466 ? 0.021, respectively. The amount of genetic divergence we have found between these taxa is remarkably similar to estimates in man, mice and Drosophila. Our results, however, indicate greater genetic divergence within the genus Taricha than was previously suspected.

Genetic variation in natural populations of five Drosophila species and the hypothesis of the selective neutrality of protein polymorphisms.

We have studied genetic variation at 30-32 loci coding for enzymes in natural populations of five species of Drosophila. The average proportion of heterozygous loci per individual is 17.7 +/- 0.4%. The average proportion of polymorphic loci per population is 69.2 +/- 2.6% or 49.8 +/- 2.2%, depending on what criterion of polymorphism is used. The following generalizations are advanced: (1) The amount of genetic polymorphism varies considerably from locus to locus. (2) At a given locus, populations of the same species are very similar in the amount and pattern of genetic variation. (3) However, at some loci large differences sometimes occur between local populations of the same species. (4) The amount of variation at a given locus is approximately the same in all five species. (5) When different species are compared, the pattern of the variation is either essentially identical or totally different at a majority of loci. We have tested the hypothesis that protein polymorphisms are selectively neutral by examining four predictions derived from the hypothesis. Our results are at variance with every one of the predictions. We have measured the amount of genetic differentiation, D, between taxa of various degrees of evolutionary divergence. The average value of D is 0.033 for local populations, 0.228 for subspecies, 0.226 for semispecies, 0.538 for sibling species, and 1.214 for morphologically distinguishable species. Our results indicate that a substantial degree of genetic differentiation (22.8 allelic substitutions for every 100 loci) occurs between allopatric populations that have diverged to the point where they might become different species if they were to become sympatric. However, very little additional genetic change is required for the development of complete reproductive isolation. After the speciation process is completed, species continue to diverge genetically from each other.

A study of gene differences between some breeds of sheep.

SummaryWith nine genetic markers of the blood, genetic distances between eight breeds of sheep was estimated after the method of Nei &amp; Roychoudury (1972). The largest distance was found between Dorset Horn and Merino and the smallest between Navajo and Suffolk. Also the average proportion of polymorphic loci in the eight breeds of sheep was estimated. The results are discussed.

Enzyme variability in the Drosophila willistoni group. VI. Levels of polymorphism and the physiological function of enzymes.

We have studied allelic variation at 28 loci coding for soluble enzymes in three sibling species of Drosophila. The average proportion of polymorphic loci per population is 58% in D. willistoni, 71% in D. equinoxialis, and 60% in D. tropicalis. An individual of any one of these three species is heterozygous at 18–22% of its genes. The correlation between the amount of polymorphism at a given locus and the equilibrium constant of the reaction catalyzed by the corresponding enzyme is not significantly different from zero. We have separated enzymes into those involved in glucose metabolism (group I) and all other enzymes (group II). The genes coding for group II enzymes are about twice as polymorphic as those coding for group I enzymes.